Corrosion is aging degradation that a metal structural material of an apparatus dissolves as ions into an environment, and important element that decides the apparatus lifetime. When corrosion proceeds, unexpected damage might be caused by the breakage of the apparatus, and corrosion protection measures are required from the viewpoint of safety. Therefore, the corrosion protection measures are taken for a variety of apparatuses used in an outdoor environment and a high temperature environment, and particularly for power plants.
The surface of a metal structural material of an apparatus to be used under a state of high temperature is generally covered with iron oxide such as Fe2O3. It is known that Fe2O3 has low solubility in water and anticorrosive effect when produced densely.
However, since the Fe2O3 film dissolves to disappear or its crystal system changes depending on the environment it is used, it might not be able to exhibit its original anticorrosion property. In view of such a problem, there is disclosed a method of the protection of the dissolution of the Fe2O3 film by using at least one of morpholine, alkanolamine and aliphatic cyclic amine as a pH adjuster to adjust the pH of water to which the Fe2O3 film is contacted. However, when the pH adjuster is used, its control is difficult, and there was a problem that the monitor of the corrosion was difficult.
There is also disclosed a method of protecting the corrosion of a boiler plant by controlling an amount of oxygen dissolved in the boiler, but there is no disclosure about the monitor of the corrosion protection of the Fe2O3 film.